1. Field of the Invention
The present invention relates to a plasma arc torch used in a continuous silicon casting apparatus, and more particularly, to an apparatus for adjusting a position of a plasma arc torch capable of adjusting positions of a plurality of plasma arc torches radially disposed about a source material introduction part through simple operation.
2. Discussion of Related Art
A silicon wafer, which has been traditionally used as a substrate for a solar cell, is manufactured by thinly cutting a directionally solidified silicon ingot. Here, quality and cost of the silicon wafer are determined by quality and cost of the silicon ingot.
Accordingly, in order to increase the quality of the silicon wafer and reduce the cost thereof, manufacturing cost of a high quality directionally solidified silicon ingot should be reduced. For this, an electromagnetic continuous casting method using a crucible formed of graphite or quartz, which is a casting material for solidifying the ingot, with no casting loss, has begun being used.
In such an electromagnetic continuous casting method, silicon, which is a source material, is a semiconductor material having a very high melting point and low electrical conductivity. Since a cooling effect caused by discharge of radiant heat is large, whereas a heating effect caused by induction heating is small, an effective supply of a heating source is needed to efficiently and continuously melt a charged source material.
An auxiliary heat source combined with a plasma arc is energized to supply a heat source. Here, a solid material, in which a plasma heat source is charged on an upper surface of a molten material, is heated to a melting point of 1414° C., and then, when surface melting occurs, heat of fusion is needed to cause a phase change to a liquid phase. Accordingly, a heating and melting process of the charged source material, which is continuously introduced, to a melting temperature, should be continuously performed.
The electromagnetic continuous casting method combined with a conventional single plasma arc torch horizontal scanning method requires a lengthy amount of time to form molten silicon for a continuous casting by melting initial solid silicon, and a side arc is generated between a plasma torch and an inner wall surface.
In addition to the side arc generated between the plasma torch and the inner wall surface, when the horizontal scanning method is used, a single torch moves to generate thermal imbalance and local variation in thermal density between areas of the source material, thereby limiting fusibility of the source material.
Further, when capacity of a horizontal scanning plasma torch is increased to improve fusibility, since calorie applied to a heating surface is excessive, volatilization of the molten silicon and generation of silicon fume (solid particles in smoke phase) increase, and thus, the fusibility and purity of the molten material decrease.